1. Field of the Invention
The invention relates to an air mass meter having a sensor element of microelectromechanical design.
2. Related Art
Air mass meters (i.e., sensors) are used, for example, in motor vehicles for determining the air mass sucked in by an internal combustion engine. Combustion can be optimized on the basis of the most reliable possible information about a sucked-in air mass by electronic control of the internal combustion engine, to the effect that a quantity of fuel which is matched precisely to the air mass is fed to the respective combustion chambers. As a result, better utilization of energy with reduced emission of pollutants is achieved.
DE 44 07 209 A1 discloses an air mass meter plugged into an intake duct for determining an air mass, wherein a defined proportion of the total flow flows through the air mass sensor.
For this purpose, the latter is embodied as a plug-in duct air mass meter. The air mass meter comprises a sensor element arranged in a measuring duct, electronics arranged in a housing for evaluating and/or detecting the measured values of the sensor element, and an outlet duct on the other side of the sensor element. For a space-saving arrangement, the specified ducts or air guiding paths are embodied in the form of a U, S or C, with the result that a device that is compact overall and is embodied as a plug-in element is formed.
An air mass meter embodied according to the teaching of WO 03/089884 A1 and embodied as a hot-film anemometer has in principle proven valuable.
During the development of modern air mass meters that operate on the basis of sensor elements embodied as microelectromechanical systems (MEMS) it has become apparent that the measurement results of the sensor elements are influenced in a particularly disadvantageous way by contamination. Contamination, caused, for example, by oil droplets in the air mass flow, results over time in a signal drift in the sensor element, which signal drift can lead to incorrect measured values for the air mass flow. However, sensor elements embodied as microelectromechanical systems have a multiplicity of advantages which should not be dispensed with.